I had an unexpected shutdown (aren't they ALL unexpected?) a week and a half ago. I left on a 40 mile journey (round trip) and as we departed about ¼ mile from my slip the engine faltered, faltered again and died. At the first falter my eye went immediately to the EWDS light display and stayed there through the second falter and shut down. The first parameter to alarm was the raw water flow after it quit (as it should have).

I immediately turned the ignition off for the protection of the coil and raised sail to maintain steering. With everything safe I could get down to business. What I knew thanks to the EWDS was I had sufficient fuel pressure and sufficient voltage to the coil. I thought about it for about a minute, especially my last refueling a few nights earlier. When I opened the fill plate to the main tank the O ring broke. Of course I didn't have a replacement (I do now), rain was forecast later that night and of course Catalina put the fuel fill plate right where water puddles on the deck. As a jury rig stopgap measure I wrapped teflon tape around the threads and tightened the fill cap. This episode led me to suspect the shutdown was due to water in the fuel tank.

I switched the tank selector valve to my secondary tank (why doesn't everybody have a second tank?), purged the lines with my electric fuel pump via the fuel polishing switch (why doesn't everybody have that too?) and tried to restart the engine. It popped and coughed telling me there was spark. I closed the raw water intake valve to avoid overfilling the waterlift and went back to starting but feathering the choke this time. After a few more coughs she fired up. I shut her down and reopened the raw water valve, restarted her and ran maybe three ½ mile laps inside outer Los Angeles Harbor as a test run. All good.

I motored over to the fuel dock, put more than enough additional fuel in the secondary tank for our planned journey and back if we had to motor the entire way and off we went. Since then I've had at least 4 hours of trouble free motoring, returned to my home slip a few days ago.

My hypothesis based on all the above: probably water in the fuel but I needed to know for sure.

I have since emptied 5 of the 12 gallons from the main tank, poured them into a 5 gallon drinking water bottle and inspected the contents. The attached picture tells the story. Next up I'll draw another 5 gallons from the tank and inspect again hoping to see no more water confirming that it was all drawn out with the first 5 gallons. I'll finish with the final 2 gallons as a double check. I was pleased to see no debris or other assorted nastiness in the fuel, just pure water.

I rebuilt the carburetor earlier today on principle. It had enough water through it to shut the engine down so opening it up was prudent. All clean inside. Following the expected successful fuel inspections I'll replace the filter.

The EWDS provided invaluable information right at the hit and saved me a ton of testing. The entire episode took maybe 5 minutes from initial failure to a running engine.

No worries Shawn. Thanks to the EWDS, two fuel tanks, an electric fuel pump with an override switch and the recent memory of a broken O ring right before rain it really was a minor inconvenience. At this stage we KNOW the problem was water in the fuel and we KNOW how it got in there. Now it's just the mechanics of repairing it so it never happens again.

My story was here is what happened, the information at hand, the hypothesis, the confirmation and the solution. I posted it in the hope it might help others someday.

The key to getting water out of the tank is to take a suction on the very bottom of the tank. The fuel pickup for the engine does NOT go to the bottom of the tank.
Access to the bottom of the tank varies from boat to boat. With my Tartan 30, I could get a piece of copper tube (about 6' long) in through the fill and to the bottom. I would then use a hand pump and pump into a gallon jug.
In these days of alcohol fuels, I found comfort in doing this once a year. No need to pump the tank dry - just get the water out of the bottom.

Good idea, think I should I should add this as one more spring commissioning tasks after a 6-7 month winter layup. Pumping out a 2-3 gallons should get any residue water out of a 18 gal tank pumping from the bottom. Good to have an old monel tank. thanks

Second five gallons of fuel removed yesterday. Clear bottle inspection showed no water. Two gallons left to remove but that will wait until I replace the deck fill plate.

Which brings me to a decision to make: does this episode point to a fuel system modification? It's a simple fact that my cartridge style water separating fuel filter passed water right through. The previous picture showed two or more quarts of water at the bottom of five gallons of fuel that had been extracted through the filter. I hafta say, I'm not too impressed with its water separating performance. However, maybe I'm expecting more than I should. A little research found that my filter is designed to separate water emulsified in the fuel. Mine was not emulsified, it was stratified. And what is a one pint filter supposed to do with two quarts of pure water? For that matter, what is any small volume filter supposed to do with two or more quarts of pure water? Time for a rethink.

I've settled on leaving the filtration as-is because:

This is the first fuel contamination shut down since I've owned the boat, over 14 years. Whatever filtration is in place and whatever I've been doing has been reliable for a long time.

We know with certainty where this water came from and it has been stopped. I much prefer stopping the contamination at its source than managing it after it's in the tank.

What can be expected with a new, different style of filter? Under the same circumstances (2 quarts of water), will a new filter do any better? Probably not so what's the point?

Neil, about all I could think to add to your system that may be of value would be a "bottom of the tank tube" to literally pump the water/??? from under the pick up.
I actually sucked the bottom of my ski boat tank every other year. I had to do this via a syphon and always got a bit of water. This was in a boat used on the Co. River in the desert. I even removed my pick-up tube on Volador 4 or 5 times in the slip with an old "Auto pulse" pump I had set up for transferring fuel while houseboating.
I also had good luck on the ski boat because I used a water separator (Fram) and then a filter/separator.

Yeah Dave, I've been brainstorming a "better mousetrap" when it comes to fuel tank design. The current thought is to form an inverted dome, sort of a bowl shaped depression formed at the lowest point in the tank and install an extraction tube that extends to the bottom of the bowl completely separate from the fuel pickup tube.

NYV, the EWDS is an acronym for MMI's Engine Warning and Diagnostic System. The system monitors 5 separate parameters while the engine is in operation and displays a warning light and audible buzzer if any of the parameters are out of a pre-determined range specific to the Atomic 4.https://moyermarine.com/product/the-...m-ktas_01_564/
You may notice some acronyms or seemingly odd terms are underlined in the posts thusly (EWDS). Placing your pointer on the underlined term without clicking displays a brief description.

As soon as my engine gave the first hint of a problem (a reduced RPM blip) my eyes went immediately to the EWDS display and stayed there throughout subsequent blips and finally shut down. No display lights illuminated until the engine stopped, then the raw water flow light illuminated first. It should have, the engine stopped, the pump stopped and the raw water was not flowing.

But what did that tell me? The monitored parameters were within specification during the episode so I knew there were no issues with engine temp, oil pressure, raw water flow and most importantly, coil input voltage and fuel supply pressure to the carburetor. So what could it be? It could be loss of spark within the ignition system or a fuel issue inside the carburetor. The recent broken fuel fill O ring followed by rain pointed me in that direction so my remedial efforts were focused there.

Second five gallons of fuel removed yesterday. Clear bottle inspection showed no water. Two gallons left to remove but that will wait until I replace the deck fill plate.

Which brings me to a decision to make: does this episode point to a fuel system modification? It's a simple fact that my cartridge style water separating fuel filter passed water right through. The previous picture showed two or more quarts of water at the bottom of five gallons of fuel that had been extracted through the filter. I hafta say, I'm not too impressed with its water separating performance. However, maybe I'm expecting more than I should. A little research found that my filter is designed to separate water emulsified in the fuel. Mine was not emulsified, it was stratified. And what is a one pint filter supposed to do with two quarts of pure water? For that matter, what is any small volume filter supposed to do with two or more quarts of pure water? Time for a rethink.

I've settled on leaving the filtration as-is because:

This is the first fuel contamination shut down since I've owned the boat, over 14 years. Whatever filtration is in place and whatever I've been doing has been reliable for a long time.

We know with certainty where this water came from and it has been stopped. I much prefer stopping the contamination at its source than managing it after it's in the tank.

What can be expected with a new, different style of filter? Under the same circumstances (2 quarts of water), will a new filter do any better? Probably not so what's the point?

I don't think a filter that can deal with water and ethanol-gas exists. My experience is they do one of two things:
1. Refuse to pass anything at all when confronted with such a mix.
2. Pass it right on through, water and all.
Racor is in the pass-it-through camp, one of my off brand filters did the opposite. I talked to a Racor engineer on the phone and he said their water separating filters were not designed for and could not deal with water and ethanol.
BTW - IMHO the entire tank is ruined, there is no saving the gas. There is water and ethanol in suspension and more that separated out.

All my water-in-fuel issues vanished when I got a new O-ring for the tank cap

Yep, exactly what happened here. I also do not use fuel dock gas. I was somewhat P.O.'ed at myself for not having spare O rings on hand. To remedy that I have:

Measured and purchased replacements from McMaster-Carr, minimum bag amount is 100. That ought to last a while. They're stored in a sealed zip-loc baggie.

Purchased and will install next week a replacement fuel fill plate for the offending main tank, an exact match to the plate I installed for my spare tank many years ago so I only have to stock one O ring size. The only difference between the two fill plates is the screw-in plugs are different colors, one black and the other red.

Neil how much total fuel do you carry and where?
A 2nd tank is an interesting idea.
Are you concerned about the additional weight?

Both tanks combined I have a 37 gallon capacity, one 12 gallon and one 25 gallon tank. My usual practice however is to carry 10 to 12 gallons in the main 12 gallon tank under the quarter berth and leave the bigger, secondary tank located in the bottom half of the cavernous port sail bin empty. For this trip I topped off the 12 gallon tank and put 5 gallons in the secondary tank as a reserve. Good thing I did too, that secondary tank came in pretty handy. If I were headed, say, to Ensenada, I'd fill both tanks so I had ample reserves no matter what. I guess the answer is, "It depends on where I'm going."

As for weight, I don't really care. I'm not a racer so an extra 1/10th of a knot is not significant to me. Besides, for Catalina trips I'm towing a 14' inflatable that costs me a full knot anyway. Hey, it's sailing. I'll get there when I get there. Good thing my slip is in the closest marina to Two Harbors at Catalina. We may not be the first to get there but we'll sure have a lot of fun on the way.

Another comment on weight, just this month I made the final touch to my all chain anchor rode: painting the waterline a little higher.

This may just be the thing to do with the enormous space aft of the quarter berth partition. I plan on adding an additional battery to starboard so it should roughly balance out. I'm also 25 gallons - another 50% would make a big difference!